Microgeneration refers to small scale systems that generate electricity and/or heat for domestic dwellings. Some systems have been commercially available for some time, for example solar thermal collectors that provide hot water and photovoltaic panels that generate electricity. A change in energy policy and recent developments in technology have prompted the emergence of micro-scale wind turbines and combined heat and power (CHP) systems. Micro generation is seen as a bold step towards decentralising power generation, reducing fuel poverty and increasing the percentage of power generated from renewable or low carbon sources.

There are many types of microgeneration systems. The following text gives a description of the main systems used to generate heat/electricity for a domestic dwelling:

Solar thermal – These systems provide hot water for a domestic property. The radiation from the sun is captured by a collector which heats cold water and returns it to the hot water tank. Depending upon the type of system and the time of year the temperature of the returned water may not be high enough for the intended use. In this case a gas-fired boiler unit is used to provide the additional energy necessary to reach the target temperature. Solar thermal systems involve modifications to the plumbing within the home and mounting of the collector unit on the roof. They have been commercially available for a number of years. Although they only provide hot water when it is sunny, they have the advantage that the solar energy is stored in the hot water tank for future use.

Photovoltaics (PV) – PV systems convert sunlight directly into electricity. There are a range of PV cells available on the market with different properties, efficiencies and cost. The cells work best in bright sunlight but do generate some electricity when it is overcast. PV cells generate DC power which requires relatively expensive electrical equipment to convert it to the 240 Volts, 50 Hertz AC electricity (UK) generally used inside buildings. PV has been commercially available for many years but the high system costs have generally only made it economic with large grants and subsidies.

Micro wind – Wind turbines use the energy from the wind to move a set of blades. This rotational movement is converted to electricity using a generator. Small wind turbines have been available for many years but mainly for generating DC electricity in off-grid applications. Due to recent advancements in technology and reduced prices turnkey AC systems are now available. Micro wind turbines are expected to perform well at exposed coastal or hilltop locations. The wind resource in the urban environment is reduced due to the complex, rough terrain. Therefore it is unlikely that micro wind will have a major impact in urban areas.

Combined heat and power (CHP) – The advent of micro CHP systems is perhaps the catalyst for the present interest in micro generation. A CHP unit provides both heat and electricity. Current systems are based on a Stirling engine. Fuel cell versions which have a more favourable electrical to thermal output ratio are expected to be available in the future. Stirling engine CHP systems are thermally operated units which replace conventional gas fired boilers in the home and use the 'waste energy' from electricity generation to heat water for building heating and general use. Overall system efficiencies in excess of 90% are possible. Micro CHP units will operate depending upon the heating demand of the house and will only generate electricity at this time. This means a performance analysis of CHP systems is difficult and the potential benefits may vary greatly for different dwellings.

Ground source heat pumps – The temperature levels several metres below the ground surface do not vary appreciably throughout the year. In the UK they are generally around 10° Celsius which can be utilised for summer cooling and winter heating. In a vertical system, a cold fluid is driven down pipes that run from the house to several 10's of meters below ground level. Horizontal systems are normally installed 2 to 3 m below ground and therefore involve less costly groundworks. However, ground temperatures are less stable at these levels and larger land take is required. The ground source energy is extracted by using conventional heat pump systems. A well designed ground source heat pump system would have a coefficient of performance (COP) of around 4.

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The UK Government's 2003 Energy White Paper envisages that the UK energy mix will include substantial amounts of micro-generation by 2020. However, if micro-generation technologies are installed at larger numbers there could be considerable disruption to the current energy system. By blurring the boundary between energy supply and demand, these technologies could change consumer-provider relationships and enable consumers to play a more active role in the energy service provision. Microgeneration presents new challenges for all stakeholders within the energy sector, including regulators, equipment suppliers and the housing and construction industries.

The Sustainable Energy Research Group undertakes research in the area of micro wind turbines, including resource assessment and turbine performance prediction. Currently the group is working on the UK's first large scale nationwide micro wind trial. In addition, the group investigates microgeneration systems in the residential sector and their impacts at an urban scale. Funding for the work on microgeneration has come from the Economic & Social Research Council (ESRC) and the Energy Saving Trust.

• Micro Wind Power Studies - UK Micro Wind Trial
• Microgeneration in the Urban Environment